Specifically, studies have demonstrated changes in DNA methylation at the BDNF promoter in blood samples from patients with Alzheimer’s disease (AD) (Rao et al., 2012; Xie et al., 2017), major depression (Januar et al., 2015; Kang et al., 2015) and schizophrenia (Ikegame et al., 2013). Here, BDNF is linked to major depressive disorder.